Intraovarian effects of androgens appear to be important regulatory factors in ovulatory failure and causing follicular atresia in growing follicles. Androgen receptors have been identified and characterized in granulosa cells. The use of an immature hypophysectomized rat treated with a single injection of pregnant mare serum gonadotropins (PMSG) will be made to obtain an animal model with sufficiently developed ovarian follicles that will respond to an LH challenge with 8-10 ova per rat. The effect of testosterone and the non-aromatizable androgen 5 alpha-dihydrostesterone (DHT) will be studied in causing follicular atresia. The inability of the atretic follicles after treatment with androgens to respond to LH with ovulation as the end point will be examined. It will also be determined if estradiol will prevent androgen induced atresia in granulosa cells. The atresia causing effects of androgens could be mediated through alterations in the 5 alpha-reductase activity, the aromatase activity, the estrogen receptors, and the binding of FSH and LH in granulosa cells. The measurement of the above mentioned changes and the time sequence of changes following a single injection of the testosterone or DHT will be carried out. It will also be examined if androgen induced follicular atresia can be prevented by stimulation of granulosa cell aromatase activity by FSH.